Various rod baffled heat exchangers have been disclosed in the art. Several of these heat exchangers have been put into successful practical application. One of the continuing problems in these heat exchangers is to establish a firm contact between the rods and the heat exchanger tubes. One proposal to solve this problem was to provide rods with areas of varying cross section and slide the rod so that an area of the rod having a small cross section is replaced by an area of a rod having a larger cross section between the tubes. Thereby the area of the rod with larger cross section gets into firm contact with the tubes. In this design rods are employed which have a special shape with alternating sections of smaller and larger cross sections. The rods also have to be longer than necessary for the heat exchanger in order to make possible the sliding movement.